In the art of electrical generator design, it is understood that magnetic and resistive losses within a stator generate heat that must be dissipated and removed to avoid electro-mechanical failure, and that these losses pose a serious constraint on the capacity of a machine of given physical dimension.
Conventional generator systems are typically cooled by air or hydrogen, both in the form of a forced convective flow within channels and turning regions. An industry requirement for the stator bars within the generator core is that the central region temperature between conducting bars not exceed a preset limit. Many factors influence the maximum central region temperature experienced in operation, including the stator bar design and insulation, the magnetic flux field, the core design, and the cooling design.
In order to reach high power density in generators, the stator core requires a certain level of cooling through stacks of lamination sheets. In conventional generators, spacer ribs or blocks are used between lamination sheets to leave room for coolant gas flow cooling ducts. Coolant gas, such as air, is forced through these cooling ducts at various intervals through the stator core by a fan. More specifically, coolant gas is conveyed from the radially outward portions of the stator core to the inward portions of the core (or vice-a-versa), thereby flowing through the core and past the stator bars. The coolant gas picks up and carries heat away from the stator core and its corresponding rotor. The heated gas may they be sent through a heat exchanger(s), where the heat is transferred to another coolant, such as water. The now cooled gas can then be recirculated to the cooling ducts, in a repeated and continuous process.
In conventional generators, the cooling ducts in the stator have either smooth walled channels, or channels with turbulators. See for example, U.S. Pat. No. 5,869,912. In U.S. Pat. No. 5,869,912, adjacent packages of stacked laminations are separated by a plurality of radially extending spacer ribs or blocks, and wherein each adjacent pair of spacer blocks define in cooperation with adjacent axially spaced laminations, a cooling duct, and a plurality of turbulator elements in each cooling duct, each turbulator element extending into the duct from one of the adjacent axially spaced laminations. The purpose of the turbulation elements is to increase the hear transfer performance, than for smooth walled channels.
While the heat transfer performance is improved with turbulation elements, a coolant pressure penalty is associated with higher friction or bluff body losses in the stator cooling ducts, such that the overall generator efficiency can be adversely impacted if the pressure drop increases as the cooling efficiency increases. In other words, turbulation elements can give rise to more friction, which in turn requires more energy to push coolant gas through the system, thereby reducing the efficiency of the generator.
It is therefore desirable to obtain a stator duct cooling system design that increases cooling efficiency, while minimizing or eliminating friction penalty losses in conventional generators. It is further desirable to increase the overall power efficiency, while maintaining the same basic stator core size.
The present invention is stator core assembly comprising adjacent packages of stacked lamination sheets that are separated by a plurality of radially extending spacer blocks, and each adjacent pair of spacer blocks define in cooperation with adjacent axially spaced laminintions, a plurality of radial cooling ducts, each duct having a least one lamination surface having plurality of concavities.
The concavities extend away from the stator core cooling ducts. The concavities enhance the degree of heat transfer between heated gas adjacent to the duct wall and relatively cooler gas near the duct centerline. This enhanced level of mixing brings cooler gas in contact with the duct wall, allowing greater heat transfer. Further, the concavities increase the surface area exposed to the coolant gas. Another feature is that at each concavity, a vortex of organized flow is created and expelled therefrom so to permit cooler gas to enter the concavity. The end result is that more cooling is achieved with the present invention because of (1) increased mixing between cooler gas and heated gas, (2) more surface area for contact between coolant gas and ducts, and (3) vortices that permit cooler gas to enter the concavity and then take away heat from the ducts.
Moreover, the design in accordance with the present invention achieves enhanced cooling, while minimizing friction losses. Thus, the present invention solves a key disadvantage of friction losses associated with designs that use turbulation elements. The present invention provides the same or similar benefits and applications as do designs having turbulation elements (see U.S. Pat. No. 5,869,912), but achieves a higher overall efficiency because it avoids or minimizes the friction losses associated with designs having turbulation elements.
The present invention can be readily incorporated into new machines or retrofitted into existing machines. The present invention can be incorporated into a broad range of generator cooling designs, as it can be applied in conjunction with any gaseous or liquid cooling medium presently in use or reasonably anticipated for future application by those skilled in the art.